Solid electrolyte-based molten lithium electrochemical cells

Abstract

Molten lithium electrochemical cells are disclosed. A solid electrolyte separates a molten lithium metal or molten lithium metal alloy from a cathode. The molten lithium cells provide high Coulombic efficiency and energy efficiency at operating temperatures less than 600° C. The cells are useful for stationary energy storage in power grids.

What is claimed is: 
     
       1. An electrochemical cell, comprising:
 an anode, wherein the anode comprises molten lithium metal or a molten lithium alloy; 
 a cathode in spaced relation to the anode, wherein the cathode is a molten Sn—Pb alloy; and 
 a solid electrolyte in a form of a cylinder positioned between the anode and the cathode, wherein the solid electrolyte is Li 7−x La 3 Zr 2−x Ta x O 12  (LLZTO), wherein x is from 0.1 to 1.0; and 
 wherein the electrochemical cell is configured to operate at a temperature ranging from 200° C. to 300° C.; 
 the solid electrolyte has a density from 99% to 99.9%; 
 the molten Sn—Pb alloy comprises from 70 mol % to 80 mol % Sn, and from 20 mol % to 30 mol % Pb, wherein mol % is based on a total mole of Sn and Pb in the molten Sn—Pb alloy; 
 the electrochemical cell exhibits a Coulombic efficiency of at least 99.0% and an energy efficiency of at least 60% at a current density of 50 mA×cm −2  and a temperature of 240° C.; and 
 a discharge cut-off capacity of the electrochemical cell is 600 mAh×cm −2 , and an amount of lithium in the cathode at the discharge cut-off capacity is from 30 mol % to 40 mol %, based on a total mole of Li, Sn, and Pb in a discharged cathode. 
 
     
     
       2. The electrochemical cell of  claim 1 , wherein the molten lithium alloy comprises Li—Al, Li—Ag, Li—Si, or Li—Sn. 
     
     
       3. The electrochemical cell of  claim 1 , wherein x is from 0.4 to 0.6. 
     
     
       4. The electrochemical cell of  claim 1 , wherein the LLZTO is selected from the group consisting of Li 6.6 La 3 Zr 1.6 Ta 0.4 O 12 , Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 , or Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 . 
     
     
       5. A power module, wherein the power module comprises one or more of the electrochemical cell of  claim 1 . 
     
     
       6. The power module of  claim 5 , further comprising a thermal source configured to heat the one or more of the electrochemical cell.